Area Forecast Discussion
Issued by NWS Greer, SC

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FXUS62 KGSP 180550
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
150 AM EDT Sat Mar 18 2017

.SYNOPSIS...
A cold front will approach the Western Carolinas later this
evening and move through the area Saturday morning. Dry high
pressure will overspread the region in the front`s wake and
persist into early next week. Another cold front is expected to
approach the forecast area from the north by the middle of next
week.

&&

.NEAR TERM /THROUGH TODAY/...
As of 150 AM EDT: The pre-frontal band of warm advection showers
will spread southeast across the area early this morning. TSRA most
likely across the mountains, but cannot be ruled out elsewhere.
There is reasonably good surface to 3 km wind shear overnight, but
surface based CAPE should be sorely lacking given the dry air east
of the mountains, so no severe thunderstorms are expected.
Otherwise, warm advection, light surface winds, and increasing cloud
cover indicate that tonight will be much warmer than recent
mornings, and around 5 degrees above climatology.

The front will sag south of the forecast area throughout the day
Saturday, bringing an end to precip chances in all areas by early
afternoon. While much drier air will return in the wake of the front
tomorrow afternoon, temperature advection will be largely
negligible, and in fact gusty W/NW downslope winds should allow most
areas to warm to about 5 degrees above normal, with a return to the
70s appearing likely across portions of the Piedmont.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...
As of 230 PM EDT Friday: it looks like the rest of the weekend and
the start of next week are shaping up to be relatively quiet. An
upper low is expected to move down across the nrn Mid-Atlantic
Region Saturday night and early Sunday. This will drive a cold
front, already on the eastern edge of the fcst area at the start of
the period, quickly to the south/east, with strong cold advection
taking hold by Saturday evening. The flow around the upper low
should give the NC mtns a brief shot of NNW flow moisture, which
should provide for a chance of precip Saturday night and early
Sunday near the TN border, mainly in the form of snow showers. No
siginificant accum is expected. Meanwhile, east of the mtns,
we should have low temps down into the frost range early Sunday,
mainly over the NC foothills and NW Piedmont.

The low level moisture should pull out and dry up early Sunday,
leaving us with a fair day as high pressure builds in from the
west. High temps will be just below normal with lots of sun. A
positively-tilted upper ridge will carry this sfc high across
the region Sunday night and Monday. Expect more frostable temps
early Monday over the NC foothills/wrn Piedmont. The high moves
away on Monday and the next system approaches from the west in the
afternoon. Think some of the model guidance is overly-optimistic
that our next system will arrive by the end of the period...00Z
Tuesday...so the fcst was kept dry. Temps will be two categories
warmer on Monday afternoon.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 245 PM Friday: A broad northwesterly flow aloft will prevail
across the forecast area, at least through the start of this cycle
in the forecast. It appears a pre-frontal trof will be situated in
our forecast area (FA) while the primary cold front will still
be well west of our region - Monday evening.

The cold front will make headway into our region late Monday night,
and then will sag slowly to along the NC/SC state line by Tuesday
evening. This slower response will allow moisture to pool, and H5
heights to fall with steepening lapse rates. We will ramp up the
POPS late Monday night in the NC mountains and over the entire
region Tuesday. SB CAPE values continue to climb with reach model
run therefore have expanded the thunder area Tuesday. We will need
to pay attention to any faster moving convection developing in the
mean NW flow aloft Tuesday. The primary forcing still appears to be
tied into low level surface convergence, and energy diving SE toward
our area in the northwesterly flow aloft.

A bit of a wrinkle in the forecast Tuesday night into Wednesday,
where the GFS is slower to push the front south, with the European
Model a little faster. We took a blend at this point in time, which
then meant hanging onto POPS Tuesday night, then ramping down
Wednesday.

There should be a lull as ridging develops Thursday, then moves off
to the east Thursday night and beyond. This sets up the start of a
potential longer period of isentropic lift as the Gulf of Mexico
opens for business.

The GFS continues to be very aggressive, while the European model is
slower and not as amplified late next week into the start of next
weekend. This far out sensible weather would indicate starting small
POPS, and later forecasts will figure whether we need to ramp them
up, ala a GFS scenario, or hold back to see how the European model
responds with later cycles of data.

Temperatures will be starting in a warming mode, ahead of the cold
front. Some areas in upstate SC may approach 80 Tuesday. Once we
have the front south of the FA, temperatures will respond with a
downward trend, as a transitory CAD regime settles in.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
At KCLT: Showers will cross the airfield early this morning. Cannot
rule out a stray in cloud lighting strike or thunder rumble, but
chance too low for the TAF. A LLWS group has been added to the TAF
given the potential for flow at 2000 feet to reach 40 to 45 kt from
the SW. Although surface winds remain SW as well, an embedded 200 ft
layer could exist with LLWS conditions met near the surface. Looks
like a period of MVFR before daybreak with some IFR after before
returning to MVFR near noon, then scattering out through the
afternoon. Winds remain SW until noon when the go WSW and gusty.
Winds turn NW and remain gusty into the evening.

Elsewhere: Similar conditions to KCLT, but with better thunder
chances at KAVL. Still not enough for the TAF. KAVL will also keep a
NW wind which becomes very gusty.

Outlook: A drier airmass will return behind the front Sunday,
continuing through at least Monday. Another cold front may bring
scattered showers and perhaps a few thunderstorms next Tuesday.

Confidence Table...

            06-12Z        12-18Z        18-24Z        00-06Z
KCLT       High  99%     Med   67%     High  95%     High 100%
KGSP       High  94%     High  85%     High 100%     High 100%
KAVL       Med   72%     Med   64%     High 100%     High 100%
KHKY       High  88%     Med   62%     High 100%     High 100%
KGMU       High  91%     High  85%     High 100%     High 100%
KAND       High  97%     Med   77%     High  94%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.FIRE WEATHER...
Moisture increases more quickly tonight ahead of a cold front which
should bring numerous to widespread showers to the area, especially
late tonight into early Saturday. The Piedmont and foothills are
expected to see rainfall amounts of .10-.25 inch, while the mtns
should see .25-.75 inch, with the highest totals expected near the
TN border.

The moist air will be very short-lived, as more dry air pushes into
the area behind the front. Meanwhile, there`s not really any cool
air behind the front, and in fact temperatures are expected to be
much warmer tomorrow. As a result, it appears likely that many areas
across the mtn valleys, Piedmont, and foothills will see RH dip to
around 25 percent, if not lower tomorrow afternoon. W/NW winds will
also become gusty tomorrow afternoon, but it does not appear that
there will be any overlap of critical RH and critical wind. Even so,
would not rule out the need for a Fire Danger Statement in some
areas tomorrow afternoon, but it seems prudent to wait and see how
the precip situation unfolds tonight before coordinating such
products.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...JPT
NEAR TERM...HG/JDL/RWH
SHORT TERM...PM
LONG TERM...TS
AVIATION...RWH
FIRE WEATHER...



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